Optical switch

ABSTRACT

An optical switch for switching the connection of one or more movable optical fibers to one or more stationary optical fibers, comprising a movable soft magnetic block connected to an end portion of each movable optical fiber, a stationary soft magnetic block connected to each stationary optical fiber and fixed at a position opposing the movable block, an actuator for moving the movable block relative to the stationary block, and a means for positioning the movable block relative to the stationary block; the actuator comprising a yoke having a base portion and a pair of arms extending from both ends of the base portion such that they sandwich the movable block in its moving direction, a permanent magnet attached to the base portion of the yoke, and a coil mounted to at least one arm; and regardless of the position of the movable block, a magnetic flux generated by the permanent magnet being more in a first gap between one arm and the movable block than in a second gap between the other arm and the movable block.

FIELD OF THE INVENTION

The present invention relates to an optical switch, particularly to anoptical switch suitable for optical communications apparatuses, lighttransmission apparatuses, etc.

BACKGROUND OF THE INVENTION

Advancing optical communications have made optical fiber communicationsnetworks have long optical paths and complicated branches. Accordingly,the switching of optical fiber paths (transmission paths) betweentelecommunications circuits has increased in optical communicationsapparatuses and light transmission apparatuses, resulting in using manyoptical switches. The purposes of switching optical paths are not onlyto switch usual telecommunications circuits, but also to recover fromtroubles by switching a broken transmission path to another normal path,to conduct the maintenance of the switching of opticaltelecommunications network lines in buildings and areas, to changeoptical paths in measuring apparatuses, etc. With respect to thebranching number of optical paths, there are a 1×2 optical switch forswitching one movable optical fiber to two stationary optical fibers, a1×m or n×m optical switch in which ends of many optical fibers areabutting, etc.

With respect to the switching systems of optical switches, there are asystem of switching light-proceeding directions by electrically oroptically changing the refractive index or phase of optical paths, asystem of switching light-proceeding directions by mechanically movingoptical paths, etc. Among them, mechano-optical switches areadvantageous in that they suffer little coupling loss of light and havelittle dependency on the wavelength of transmitted light. Accordingly,proposals have been made to provide mechano-optical switches havingvarious structures depending on various switching purposes and branchingnumbers.

For instance, a mechano-optical switch described in U.S. Pat. No.6,169,826 comprises, as shown in FIG. 11, a movable member 30 made of asoft magnetic ceramic, to which end portions of two movable opticalfibers 20 a, 20 b are fixed, a stationary member 32 fixed at a positionopposing the movable member 30, four stationary optical fibers 21 a, 21b, 21 c, 21 d fixed to the stationary member 32, an actuator for movingthe movable member 30 relative to the stationary member 32, and a meansfor positioning the movable optical fibers 20 a, 20 b relative to thestationary optical fibers 21 a, 21 b, 21 c, 21 d, the actuatorcomprising a permanent magnet 52, first and second yokes 50 a, 50 bopposing each other such that they sandwich the movable member 30 in itsmoving direction, and coils 51 a, 51 b mounted to the first and secondyokes 50 a, 50 b. This small, high-reliability mechano-optical switch isnow widely used.

Optical telecommunications networks are classified to telecommunicationsnetworks of analog lines (called “telecommunications lines”) includinglong-distance communications between cities, and closedtelecommunications networks in companies, etc. [generally called “localarea networks (LAN)”]. Some telecommunications networks of analog lineshave optical fibers for redundant circuits to minimize troubles by thedisruption of optical fibers, with many optical switches used forswitching between these optical fibers for redundant circuits. Opticalswitches for this purpose have a self-holding mechanism consumingelectric power only during switching but needing no electric power whenoptical fibers are coupled. Described in U.S. Pat. No. 6,169,826 as anoptical switch suitable for such applications is a latching opticalswitch comprising movable optical fibers which are moved by energizingcoils and held at that position by a permanent magnet.

The LAN-type optical telecommunications network has a closed light loopas a whole, with optical fibers connected by terminal devices on theloop. Introduced light signals are once converted to electric signals,and electric signals passing through copper lines from the terminaldevices are subjected to necessary treatments for transmitting to orreceiving from a LAN, converted to light signals and then return to theloop. Though there is no problem in this telecommunications network aslong as each terminal works normally, the failure of one terminal stopslight signals from being sent, resulting in the breakdown of the entiretelecommunications network. To prevent this problem, an optical switchfor cutting the failed terminal away from the light loop at the time ofabnormality should be provided. In this case, a non-latching opticalswitch in which movable optical fibers automatically return to apredetermined “home position” when a normal electric signal is stoppedis more preferable than the above latching optical switch in whichmovable optical fibers are kept at a holding position. Though theoptical switch described in U.S. Pat. No. 6,169,826 has a small,high-reliability structure using an electromagnetic force for switchingoperation, it is not a non-latching type. It may be contemplated to usea spring force for returning without electric power, but the structureof the electromagnetically operated optical switch described in U.S.Pat. No. 6,169,826 would become complicated if a spring mechanism isadded thereto.

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide a small,high-reliability, non-latching optical switch having movable opticalfibers that can move to a home position at the time of abnormality.

DISCLOSURE OF THE INVENTION

The optical switch for switching the connection of one or more movableoptical fibers to one or more stationary optical fibers according to anembodiment of the present invention comprises a movable soft magneticblock connected to an end portion of each movable optical fiber, astationary soft magnetic block connected to each stationary opticalfiber and fixed at a position opposing the movable block, an actuatorfor moving the movable block relative to the stationary block, and ameans for positioning the movable block relative to the stationaryblock; the actuator comprising a yoke having a base portion and a pairof arms extending from both ends of the base portion such that theysandwich the movable block in its moving direction, a permanent magnetattached to the base portion of the yoke, and a coil mounted to at leastone arm; and regardless of the position of the movable block, a magneticflux generated by the permanent magnet being more in a first gap betweenone arm and the movable block than in a second gap between the other armand the movable block.

The first and second gaps preferably have different widths in the movingdirection of the movable block.

The optical switch for switching the connection of one or more movableoptical fibers to one or more stationary optical fibers according toanother embodiment of the present invention comprises a movable softmagnetic block connected to an end portion of each movable opticalfiber, a stationary soft magnetic block connected to each stationaryoptical fiber and fixed at a position opposing the movable block, anactuator for moving the movable block relative to the stationary block,and a means for positioning the movable block relative to the stationaryblock; the actuator comprising a yoke having a base portion and a pairof arms extending from both ends of the base portion such that theysandwich the movable block in its moving direction, a permanent magnetfixed between the stationary block and the yoke, and one or more coilsmounted to the yoke; the movable block moving between a home positionclosest to one arm and a make position closest to the other arm; thewidth (a+s) of the first gap being smaller than the width (b−s) of thesecond gap at the make position, wherein a represents the width of thefirst gap between the movable block and the one arm at the homeposition, b represents the width of the second gap between the movableblock and the other arm at the home position, and s represents themoving distance of the movable block.

The difference (b−a−2s) between the width (a+s) of the first gap and thewidth (b−s) of the second gap is preferably 0.3 mm or more at the makeposition.

The optical switch for switching the connection of one or more movableoptical fibers to one or more stationary optical fibers according to afurther embodiment of the present invention comprises a movable softmagnetic block connected to an end portion of each movable opticalfiber, a stationary soft magnetic block connected to each stationaryoptical fiber and fixed at a position opposing the movable block, anactuator for moving the movable block relative to the stationary block,and a means for positioning the movable block relative to the stationaryblock; the actuator comprising a yoke having a base portion and a pairof arms extending from both ends of the base portion such that theysandwich the movable block in its moving direction, a permanent magnetattached to the yoke, and a coil mounted to at least one arm; and thepermanent magnet being positioned away from a longitudinal center lineextending between the pair of arms.

With the above structure, a magnetic flux generated by the permanentmagnet flows through a first magnetic flux path from the permanentmagnet to the stationary block, to the movable block, to the first gapand to the one arm, and a second magnetic flux path from the permanentmagnet to the other arm, to the second gap, to the movable block, to thefirst gap and to the one arm. Accordingly, the magnetic flux from thepermanent magnet is always more in the first gap than in the second gap.

The movable block moves between a home position closest to one arm and amake position closest to the other arm. When the coil is energized togenerate a magnetic flux, the total magnetic flux is less in a first gapbetween the movable block and one arm than in a second gap between themovable block and the other arm, so that the movable block is held atthe make position. When the coil becomes inactive, the movable blockreturns to the home position.

A setback distance δ expressed by δ=(b−s)−a is preferably more than 0,wherein a and b respectively represent the widths of the first andsecond gaps at the home position, and s represents the moving distanceof the movable block. This optical switch has higher reliability inautomatic returning to a home position than the optical switch meetingthe relation of b=(a+s).

The coil is preferably mounted to each arm of the yoke.

At least one of the movable block and the stationary block is preferablymade of a soft magnetic ceramic. The soft magnetic ceramic is preferablya soft magnetic ferrite, more preferably manganese-zinc ferrite. When asingle crystal ferrite is used as the soft magnetic ferrite, workingprecision is easily improved.

The optical switch preferably comprises pluralities of movable opticalfibers and/or stationary optical fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a plan view showing an optical switch according to thefirst embodiment of the present invention;

FIG. 1(b) is an exploded view showing an important portion of theoptical switch of FIG. 1(a);

FIG. 1(c) is a cross-sectional view taken along the line C-C in FIG.1(b);

FIG. 2(a) is an enlarged cross-sectional view taken along the line A-Ain FIG. 1(a);

FIG. 2(b) is an enlarged cross-sectional view taken along the line B-Bin FIG. 1(a);

FIG. 3(a) is a schematic view showing the magnetic flux of a permanentmagnet when a movable block is held at a home position in the opticalswitch of FIG. 1(a);

FIG. 3(b) is a schematic view showing the magnetic flux of a permanentmagnet and the magnetic flux of coils when the movable block is beingchanged from the home position to a make position in the optical switchof FIG. 1(a);

FIG. 3(c) is a schematic view showing the distance between a movableblock and a tip yoke member when the movable block is held at a makeposition in the optical switch of FIG. 1(a);

FIG. 4 is a graph showing the relation between a setback distance and amagnetic attraction force in an air gap in Example 1;

FIG. 5 is a graph showing the relation between the magnetomotive forceof a coils and a magnetic attraction force in an air gap in Example 1;

FIG. 6 is a plan view showing an optical switch according to the secondembodiment of the present invention;

FIG. 7(a) is a schematic view showing the magnetic flux of a permanentmagnet when a movable block is held at a home position in the opticalswitch of FIG. 6;

FIG. 7(b) is a schematic view showing the magnetic fluxes of a permanentmagnet and coils when a movable block is moving from a home position toa make position in the optical switch of FIG. 6;

FIG. 7(c) is a schematic view showing the distance between a movableblock and a tip yoke member when the movable block is held at a makeposition in the optical switch of FIG. 6;

FIG. 8 is a plan view showing an optical switch according to the thirdembodiment of the present invention;

FIG. 9(a) is a schematic view showing the magnetic flux of a permanentmagnet when a movable block is held at a home position in the opticalswitch of FIG. 8;

FIG. 9(b) is a schematic view showing the magnetic fluxes of a permanentmagnet and coils when a movable block is moving from a home position toa make position in the optical switch of FIG. 8;

FIG. 9(c) is a schematic view showing the distance between a movableblock and a tip yoke member when the movable block is held at a makeposition in the optical switch of FIG. 8;

FIG. 10 is a graph showing the relation between the magnetomotive forceof coils and a magnetic attraction force in Example 3; and

FIG. 11 is a plan view showing a conventional optical switch describedin U.S. Pat. No. 6,169,826.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [I] First Embodiment

As an example of the non-latching optical switch of the presentinvention operated by an electromagnetic force, a 2×4 optical switchwill be explained referring to FIGS. 1-3. Fixed to a non-magneticsubstrate 15 are an electromagnetic actuator 10 for moving a movableblock 5, and a block 4 for supporting movable optical fibers 2 a, 2 b.The substrate 15 need only be non-magnetic, and it may be formed bynon-magnetic materials such as stainless steel, ceramics, glass, etc.The electromagnetic actuator 10 comprises a soft magnetic yoke 1 madeof, for instance, soft magnetic iron or Parmalloy, a stationary softmagnetic block 6 made of, for instance, soft magnetic ceramics such assoft magnetic ferrite, a permanent magnet 8 made of, for instance, anneodymium-iron-boron alloy, and coils 9 a, 9 b. The support block 4 andthe stationary block 6 are fixed to the substrate 15, such that themovable optical fibers 2 are in parallel with the stationary opticalfibers 3.

The soft magnetic yoke 1 is preferably in a U or E shape, etc., having apair of arms. FIG. 1(a) shows a U-shaped yoke having a pair of arms 1 a,1 b extending from both ends of a base portion 1 c such that theysandwich the movable block 5. A stationary block 6 is fixed to a centerof the base portion 1 c of the yoke 1 via the permanent magnet 8. Thestationary block 6 may be directly fixed to the base portion 1 c. Thepermanent magnet may be made of neodymium-iron-boron magnets, or othertypes of permanent magnets such as samarium-cobalt magnets, etc., andthe neodymium-iron-boron magnets are more preferable because of a highresidual magnetic flux density. The stationary block 6 supports the endportions of the stationary optical fibers 3 a, 3 b, 3 c, 3 d, such thatthey oppose the end portions of the movable optical fibers 2 a, 2 b.

The coils 9 a, 9 b are mounted to the arms 1 a, 1 b of the yoke 1.Though one coil may be mounted to the yoke 1, it is preferably mountedto each arm 1 a, 1 b for easy control of a magnetic flux and forsecuring a winding space. Each plate-shaped tip yoke member 1 d, 1 e isattached to the inner surface of each arm 1 a, 1 b of the yoke 1 in atip end portion, such that it is opposite to each side surface of themovable block 5 with a predetermined gap.

The coils 9 a, 9 b are energized to generate a magnetic flux flowingthrough the yoke 1 and the movable block 5. The amount of a magneticflux can be controlled by changing the ON/OFF, polarity, amount, etc. ofelectric current supplied to the coils 9 a, 9 b. The movable opticalfibers can be switched to either one of an unlatched state(non-self-holding state) or a latched state (self-holding state) byturning on and off the coils 9 a, 9 b.

As shown in FIG. 2(a), the stationary block 6 comprises a soft magneticblock body 6 a, and a glass-made cover plate 6 b fixed to the block body6 a. The soft magnetic block body 6 a is provided on an upper surfacewith four V-shaped grooves 23 for fixing four stationary optical fibers3 a, 3 b, 3 c, 3 d, and V-shaped grooves 71, 71 on both sides for fixingtwo positioning pins 7 a, 7 b made of a hard metal in parallel. Thelongitudinal direction of the optical fibers is designated as an X-axisdirection, and its perpendicular direction is designated as a Y-axisdirection.

As shown in FIGS. 1(b) and 2(b), a movable block 5 opposing thestationary block 6 with a predetermined gap comprises a soft magneticblock body 5 a, and a glass-made cover plate 5 b fixed thereto. Theblock body 5 a is provided on an upper surface with two V-shaped grooves23 for fixing two movable optical fibers 2 a, 2 b, and trapezoidalgrooves 72 a, 72 b for receiving two positioning pins 7 a, 7 b inparallel. Each groove 72 a, 72 b has a width making the pins 7 a, 7 bmovable over the same distance as the switching distance s of thestationary optical fibers 3 a, 3 b, and 3 c, 3 d. The movable block 5supports the tip end portions of the movable optical fibers 2 a; 2 b,and the positioning pins 7 a, 7 b received in the trapezoidal grooves 72a, 72 b make the block 5 movable in a Y-axis direction by the distances. Each part in the optical switch 1 is as high as, for instance, shownin FIG. 1(c).

Both of the movable block 5 and the stationary block 6 are made of softmagnetic materials. To have a sufficient magnetic attraction to the yoke1, the soft magnetic materials preferably have a saturation magneticflux density of 0.3 T (3 kG) or more. The soft magnetic materials arepreferably soft magnetic ceramics, particularly soft magnetic ferrite.Because the soft magnetic ferrite can be worked at high precision andhas a thermal expansion coefficient closer to that of glass formingoptical fibers than those of soft magnetic metals, it provides ahigh-reliability optical switch. Also, because the soft magnetic ferritehas a lower density than those of soft magnetic metals, it is suitablefor the movable block 5. When the holder 4 is also formed by the samesoft magnetic ferrite, there is no difference in a thermal expansioncoefficient among the holder 4, the movable block 5 and the stationaryblock 6, so that no positional discrepancy occurs in the optical fibersby temperature change on both movable and stationary sides.

The preferred soft magnetic ferrite is manganese-zinc ferrite,nickel-zinc ferrite, etc. The manganese-zinc ferrite is particularlypreferable because of high permeability and saturation magnetic fluxdensity.

With end portions of the movable optical fibers 2 a, 2 b and thestationary optical fibers 3 a, 3 b, 3 c, 3 d near their connectionssupported by the movable block 5 and the stationary block 6, thepositional discrepancy of the optical fibers can be prevented duringoperation, resulting in high positioning accuracy. In addition, becausethe movable block 5 made of soft magnetic ferrite suffers little elasticdeformation, its positional discrepancy and warpage can be suppressedduring the operation even if it is made small and thin.

Because the trapezoidal grooves 72 a, 72 b of the movable block 5regulate a range in which the positioning pins 7 a, 7 b can move, bothends of the trapezoidal grooves 72 a, 72 b function as stoppers for themovable block 5, thereby positioning the movable optical fibers 2 to thestationary optical fibers 3. The trapezoidal grooves 72 a, 72 b alsofunction as vertical guides when the movable block 5 moves in a Y-axisdirection. Incidentally, the positioning of the movable block 5 can beachieved not only by a combination of the positioning pins 7 a, 7 b andthe trapezoidal grooves 72 a, 72 b, but also by guides, stoppers, etc.disposed outside the movable block 5.

The optical switch in this embodiment meets the requirements of a<b, and(a+s)<(b−s), wherein a represents the width of an air gap Ga (first gap)between the movable block 5 and the tip yoke member 1 d at a homeposition, b represents the width of an air gap Gb (second gap) betweenthe movable block 5 and the tip yoke member 1 e at a home position, ands represents the moving distance of the movable block 5. Accordingly,when no electric current is supplied to the coils 9 a, 9 b, a magneticflux passes always more through the air gap Ga than through the air gapGb, so that the movable block 5 is attracted toward the tip yoke member1 d. At this time, it is said that the movable block 5 is at a homeposition. The movable block 5 is held on the side of the tip yoke member1 d at the home position, so that the movable optical fiber 2 a isconnected to the stationary optical fiber 3 a, and that the movableoptical fiber 2 b is connected to the stationary optical fiber 3 c.

In FIG. 3(a), the flow of a magnetic flux generated by the permanentmagnet 8 at a home position is shown by black arrows. For theclarification of explanation, the distances between the movable block 5and the tip yoke members 1 d, 1 e are exaggerated. The magnetic fluxgenerated by the permanent magnet 8 flows through a first magnetic fluxpath of stationary block 6→movable block 5→tip yoke member 1 d→arm 1a→base portion 1 c→permanent magnet 8, and a second magnetic flux pathof stationary block 6→movable block 5→tip yoke member 1 e→arm 1 b→baseportion 1 c→permanent magnet 8. Because the width a of the air gap Ga issufficiently smaller than the width b of the air gap Gb at the homeposition, a magnetic flux passing through the air gap Ga is much morethan a magnetic flux passing through the air gap Gb. Because a magneticattraction force F expressed by the formula: F=Φ²/2μA, wherein Φrepresents the amount of a magnetic flux passing through an air gap, Arepresents the area of the air gap, and μ is the permeability of the airgap, is proportional to the square of the magnetic flux, the movableblock 5 is surely attracted toward the tip yoke member 1 d.Incidentally, the “air gap” means a space between magnetic bodies, whichmay be filled with a gas such as air, etc., or a liquid such as amatching oil, etc.

Because there are the movable block 5, the stationary block 6 and thepermanent magnet 8 inside the yoke 1 between both arms 1 a, 1 b in theoptical switch in this embodiment, the magnetic flux from the permanentmagnet 8 is prevented from leaking. Accordingly, a magnetic flux can beintroduced into air gaps between the movable block 5 and both arms 1 a,1 b more efficiently in this optical switch than in an optical switchcomprising no stationary block so that magnetic poles of the permanentmagnet are open. Such arrangement is suitable for having different gapsbetween the movable block 5 and a pair of arms 1 a, 1 b. Thus, amagnetic circuit formed by the permanent magnet 8 is divided to a firstmagnetic flux path having a larger amount of a magnetic flux and asecond magnetic flux path having a smaller amount of a magnetic flux,resulting in different attraction forces to the movable block 5. As aresult, when the coils 9 a, 9 b are not energized, the movable block 5is surely held at the home position.

FIG. 3(b) shows switching from a home position to a make position.Supplied to the coils 9 a, 9 b is electric current for generating amagnetic flux shown by white arrows, which cancels the magnetic fluxfrom the permanent magnet 8 in the air gap Ga, and enhances the magneticflux from the permanent magnet 8 in the air gap Gb. Though the coils 9a, 9 b may be separately controlled, it is preferable for the simplicityof control to connect the coils 9 a, 9 b in series such that the sameelectric current flows therethrough. The magnetic flux generated by thecoils 9 a, 9 b flows through a path of yoke 1→tip yoke member 1d→movable block 5 tip yoke member 1 e→yoke 1. Accordingly, the movableblock 5 moves from the side of the tip yoke member 1 d to the side ofthe tip yoke member 1 e (make position) by the magnetic flux passingthrough both air gaps Ga, Gb (the magnetic flux from the permanentmagnet 8+the magnetic flux of the coils 9 a, 9 b). At the make position,the movable optical fiber 2 a is coupled to the stationary optical fiber3 b, and the movable optical fiber 2 b is coupled to the stationaryoptical fiber 3 d.

FIG. 3(c) shows the width of each air gap Ga, Gb when the movable block5 is at the make position. As described above, though the width (a+s) ofthe air gap Ga is sufficiently smaller than the width (b−s) of the airgap Gb at the make position, the magnetic flux generated by the coils 9a, 9 b makes the total magnetic flux passing through the air gap Ga lessthan the total magnetic flux passing through the air gap Gb, so that themovable block 5 is kept attracted toward the tip yoke member 1 e andthus held at the make position. Thus, the formation of two magneticpaths enables the operation of the electromagnetic actuator 10 by smallelectric current. Particularly when two coils 9 a, 9 b are connected inseries, the operation can be conducted by extremely small electriccurrent. As a result, electricity consumption can be extremelysuppressed even in a non-latching optical switch that should beenergized to keep the make position.

When electric current is not supplied to the coils 9 a, 9 b by thebreakdown of current-supplying signals, power breakdown, etc., the coils9 a, 9 b stops generating a magnetic flux, leaving only the magneticflux from the permanent magnet 8. Thus, the movable block 5 is put inthe state shown in FIG. 3(a), returning to the home position byattraction toward the tip yoke member 1 d. Thus, the movable block 5 isheld at the make position while a terminal device is operated normally,but when electric signals or electric energy is not supplied byabnormality in the terminal device, the movable block 5 cannot be heldat the make position, automatically returning to the home position. Thisnon-latching operation is achieved by meeting (a+s)<(b−s). In order thatthe movable block 5 is surely switched to the home position despite alarge mass or the influence of gravity, the difference (b−a−2 s) betweenthe width (a+s) of the air gap Ga and the width (b−s) of the air gap Gbat the make position is preferably 0.3 mm or more.

In the case of the self-holding optical switch (U.S. Pat. No.6,169,826), an air gap Gb between a tip yoke member 1 e shown by aphantom line in FIG. 3(c) and a movable block 5 has a width a. In theoptical switch of this embodiment, however, the air gap Gb has a width(b−s). Accordingly, the setback distance δ is [(b−s)−a]. The differencebetween the width of the air gap Ga and the width of the air gap Gb hascorrelation with the setback distance δ.

[2] Second Embodiment

The optical switch in the second embodiment comprises a permanent magnetattached to part of the yoke. Accordingly, the requirements of(a+s)<(b−s), and δ[=(b−s)−a]>0 need not be met. A specific example ofthis optical switch is shown in FIGS. 6 and 7. The same referencenumerals are assigned to the same parts as in the first embodiment, andtheir explanations will be omitted.

As shown in FIG. 6, a substantially E-shaped yoke 1 having a pair ofarms 1 a, 1 b is provided with a projection 1 f at a center of its baseportion 1 c, and a permanent magnet 8 is arranged in the base portion 1c at a position deviated toward the arm 1 a from a longitudinal centerline 40 extending at the middle of a pair of arms 1 a, 1 b. FIG. 7(a)shows a state in which a movable block 5 is held at a home position onthe side of a tip yoke member 1 d. In this state, a magnetic fluxgenerated by the permanent magnet 8 shown by black arrows is divided toa first magnetic flux path of base portion 1 c→stationary block6→movable block 5→tip yoke member 1 d→arm 1 a, and a second magneticflux path of base portion 1 c→arms 1 b→tip yoke member 1 e→movable block5→tip yoke member 1 d→arm 1 a. Instead of mounting the permanent magnet8 in the base portion 1 c, it may be mounted at a position of the tipyoke member 1 d.

While there is only the second magnetic flux path in the air gap Gbbetween the tip yoke member 1 e and the movable block 5, the air gap Gabetween the movable block 5 and the tip yoke member 1 d has the firstand second magnetic flux paths, resulting in a sufficiently largeramount of a magnetic flux in the air gap Gb than in the air gap Ga. Thedifferent amounts of a magnetic flux result in difference in a magneticattraction force, so that while no electric current is supplied to thecoils 9 a, 9 b, the movable block 5 is held on the side of the tip yokemember 1 d to connect a movable optical fiber 2 a to a stationaryoptical fiber 3 a, and a movable optical fiber 2 b to a stationaryoptical fiber 3 c.

FIG. 7(b) shows the switching from a home position to a make position.Because a magnetic flux (shown by white arrows) generated from thecurrent-supplied coils 9 a, 9 b is opposite in direction to the magneticflux from the permanent magnet 8, and sufficiently larger than thelatter, the total magnetic flux is sufficiently more in the air gap Gbthan in the air gap Ga. Thus, the movable block 5 can be held at themake position only by supplying current to the coils 9 a, 9 b.

FIG. 7(c) shows the widths of the air gaps Ga, Gb when the movable block5 is at the make position. The depicted example meets the requirement of(a+s)=b, but it is not indispensable. Though the widths of the air gapsGa, Gb at the make position are (a+s) and (b−s), respectively, themagnetic flux from the permanent magnet 8 is sufficiently more in theair gap Ga than in the air gap Gb. Accordingly, when the supply ofelectric current to the coils 9 a, 9 b stops by the breakdown of signalsof supplying current to the coils, power breakdown, etc., the movableblock 5 automatically returns to the home position on the side of thetip yoke member 1 d. When the operation of a terminal device is turnednormal, the movable block 5 moves to and held at the make position bythe magnetic flux generated by the coils 9 a, 9 b. Accordingly, theoptical switch of this embodiment is also a non-latching optical switch.

Third Embodiment

The third embodiment does not differ from the second embodiment exceptfor meeting the requirements of (a+s)<(b−s), and δ[=(b−s)−a]>0. Thus,the same reference numerals are assigned to the same parts as in thesecond embodiment, and their explanations will be omitted. FIG. 8 showsthe optical switch of the third embodiment at a home position. A tipyoke member 1 e is thinner than the tip yoke member of the secondembodiment (shown by a chain line) by a setback distance δ. As shown inFIGS. 9(a) and (c), when the movable block 5 is at a make position, thewidths of air gaps Ga, Gb are (a+s) and (b−s), respectively, wherein aand b represent the widths of the air gaps Ga, Gb when the movable block5 is at a home position, and s represents the moving distance of themovable block 5. The setback distance δ is expressed by [(b−s)−a].

In the third embodiment, because the air gap Gb is wider than that inthe second embodiment by a setback distance δ, the magnetic flux fromthe permanent magnet 8 (shown by black arrows) passes through the airgap Ga more in the third embodiment than in the second embodiment, andthrough the air gap Gb less in the third embodiment than in the secondembodiment. Accordingly, when no electric current is supplied to thecoils 9 a, 9 b, the movable block 5 is held at the home position on theside of the tip yoke member 1 d more strongly in the third embodimentthan in the second embodiment.

FIG. 9(b) shows switching from the home position to the make position.When electric current is supplied to the coils 9 a, 9 b to generate amagnetic flux (shown by white arrows), the magnetic flux (shown by blackarrows) from the permanent magnet 8 and the magnetic flux (shown bywhite arrows) from the coils 9 a, 9 b cancel each other in the air gapGa, and the magnetic flux from the coils 9 a, 9 b is sufficiently morethan the magnetic flux from the permanent magnet 8 in the air gap Gb.Accordingly, the total magnetic flux is more in the air gap Gb than inthe air gap Ga, thereby moving the movable block 5 from the side of thetip yoke member 1 d to the side of the tip yoke member 1 e.

FIG. 9(c) shows the widths of the air gaps Ga, Gb when the movable block5 is at the make position. Because they are the same as in the firstembodiment, their explanation will be omitted. As described above,because the magnetic flux from the permanent magnet 8 (shown by blackarrows) passes through the air gap Ga more in the third embodiment thanin the second embodiment, and through the air gap Gb less in the thirdembodiment than in the second embodiment, the movable block 5 returns toand is held at the side of the tip yoke member 1 d more strongly than inthe second embodiment, when electric current is not supplied to thecoils 9 a, 9 b by the breakdown of signals for supplying current to thecoils, power breakdown, etc.

Because the magnetic flux generated by the permanent magnet 8 is dividedto a path passing through only one arm 1 a, and a path passing throughboth arms 1 a, 1 b in the second and third embodiments, in either of acase (a) meeting the requirement of (a+s)=b as shown in FIGS. 6 and 7,and a case (b) meeting the requirements of (a+s)<(b−s), andδ[=(b−s)−a]>0 as shown in FIGS. 8 and 9, the magnetic flux from thepermanent magnet 8 is more in the air gap Ga on the side of the arm 1 athan in the air gap Gb on the side of the arm 1 b. In this respect,there is no difference from the first embodiment in which the permanentmagnet 8 is mounted to a center of the base portion 1 c of the yoke 1.

In any of the above optical switches, the magnetic flux from thepermanent magnet 8 is more in the air gap Ga than in the air gap Gb, sothat the movable block 5 is held at the home position when the coils 9a, 9 b are not energized. Because the total magnetic flux is less in theair gap Ga than in the air gap Gb while the coils 9 a, 9 b areenergized, the movable block 5 is held at the make position. However,when current supply to the coils 9 a, 9 b is stopped, the movable block5 automatically returns to the home position. Accordingly, the opticalswitch of this embodiment is also a non-latching optical switch.

Various modifications may be added unless they are deviated from theidea of the present invention. For instance, the yoke is in an E shapein the above embodiment, but this is not restrictive. The yoke need onlyhave substantially parallel arms, and it may be, for instance, in a Ushape. The arms and the base portion of the yoke may be integral, orthey may be separate parts. Also, integral L-shaped arms may be abuttedto the base portion.

The permanent magnet may be sandwiched by adjacent yoke portions, forinstance, in the case of an assembled yoke, or mounted to a recess inthe case of an integral yoke.

To movably receive pins for positioning at the home position and themake position, grooves formed in the block bodies of the movable blockand the stationary block are not restricted to be trapezoidal, but maybe square in cross section. Grooves for fixing the optical fibers andgrooves for receiving the pins may be formed in the block body and/orthe cover plate.

Instead of using two different-thickness tip yoke members, the setbackdistance δ may be obtained by adjusting the positions of both arms. Theposition adjustment of both arms may be achieved by soft magneticspacers disposed between the arms and the base portion of the yoke. Inthis case, the tip yoke members may be eliminated. To make the amountsof the magnetic flux passing through the air gaps Ga, Gb unequal, theyoke may be provided with a gap at a position deviated from thelongitudinal center line 40, or a non-magnetic body or alow-permeability body may be inserted into the gap.

The cover plate is not restricted to being made of glass, but may bemade of the same soft magnetic ceramics as those of the movable blockand the stationary block to have the same thermal expansion coefficient.

The present invention will be explained in further detail referring toExamples below, without intension of restricting the present inventionthereto.

EXAMPLE 1

The operation of the optical switch shown in FIG. 1 was tested. All of asupport block 4, a movable block 5 and a stationary block 6 were made ofmanganese-zinc ferrite having a saturation magnetic flux density of 0.47T (4,700 G), a permeability of 1,500 (at 1 kHz) and a thermal expansioncoefficient of 115×10⁻⁷/° C. The movable block 5 was as thick as 1.9 mm,and as wide as 3 mm in an X-axis direction and 2.5 mm in a Y-axisdirection. Each tip yoke member 1 d, 1 e made of SS400 (JIS) had anattraction surface of 2 mm×1.9 mm, opposing the movable block 5 in aY-axis direction. Each coil 9 a, 9 b had 500 turns. At a home position,the width a of the air gap Ga between the tip yoke member 1 d and themovable block 5 was 0.075 mm, and the moving distance s of the movableblock 5 was 0.25 mm.

With no electric current supplied to the coils 9 a, 9 b, the width b ofthe air gap Gb was increased to measure a magnetic attraction force inthe air gaps Ga, Gb. The results are shown in FIG. 4. The magneticattraction force was defined as “plus” in a direction to the homeposition and “minus” in a direction to the make position.

As is clear from FIG. 4, when the magnetic attraction force was zero atthe make position (switching occurred from the make position to the homeposition), a setback distance [(b−s)−a] was about 0.25 mm. At this time,a+s=0.325 mm, and b−s=δ+a=0.325 mm. Accordingly, when the setbackdistance is set more than 0.25 mm, the condition of (a+s)<(b−s) is met,always generating a force of returning to the home position. When thesetback distance δ is 0, it is a self-holding optical switch.

With the setback distance changed to 0.3 mm, the coils 9 a, 9 b wereenergized to measure a magnetic attraction force at the home positionand the make position. The results are shown in FIG. 5. As is clear fromFIG. 5, when electric current of about 30 A·T or more is supplied toeach coil 9 a, 9 b, the movable block 5 can be moved from the homeposition to the make position.

A Transmitting light loss was as small as −0.5 dB between −20° C. and+80° C.

EXAMPLE 2

The operation of the same optical switch as in Example 1 except that thewidth of a movable block 5 was 2 mm in an X-axis direction and 3.2 mm ina Y-axis direction width was tested, with a setback distance δ changedfrom 0.5 mm to 0.7 mm and to 0.75 mm, namely [(b−s)−(a+s)] changed from0.25 mm to 0.45 mm and to 0.5 mm. As a result, when the setback distanceδ was 0.7 mm and 0.75 mm, namely when [(b−s)−(a+s)] was 0.45 mm and 0.5mm, a non-latching operation was surely conducted. However, when thesetback distance δ was 0.5 mm, namely when [(b−s)−(a+s)] was 0.25 mm,the magnetic attraction force was too small to always conduct anon-latching operation. It is thus clear that the difference (b−a−2s)between the width (a+s) of the air gap Ga and the width (b−s) of the airgap Gb is preferably 0.3 mm or more. The transmitting light loss was assmall as in Example 1.

EXAMPLE 3

The operation of the optical switch shown in FIG. 6 with a movable block5 as thick as 1.9 mm and as wide as 3 mm in an X-axis direction and 2.5mm in a Y-axis direction was tested. Each tip yoke member 1 d, 1 e madeof SS400 (JIS) had an attracting surface of 2 mm in width and 1.9 mm inthickness, opposing the movable block 5 in a Y-axis direction. Each coil9 a, 9 b had 500 turns. At a home position, the width a of the air gapGa between the tip yoke member 1 d and the movable block 5 was 0.075 mm,the width b of the air gap Gb between the tip yoke member 1 e and themovable block 5 was 0.325 mm, and the width of an air gap between themovable block 5 and the stationary block 6 was 0.35 mm. The movingdistance s of the movable block 5 was 0.25 mm.

With the same amount of electric current supplied to both coils 9 a, 9b, a magnetic attraction force was measured at the movable block 5 andthe tip yoke member at the home position and the make position,respectively. The results are shown in FIG. 10. The magnetic attractionforce at the home position was 0 at about 65 A·T. It is clear that whenmore electric current is supplied, it is turned to the make position. Itis also clear that when electric current is shut off, the magneticattraction force becomes plus even at the make position, so that itautomatically returns to the home position. The transmitting light losswas as small as in Example 1.

EFFECT OF THE INVENTION

As described above, in the non-latching optical switch of the presentinvention for moving movable optical fibers by an electromagnetic forceto mechanically switch optical paths, which is small and high inprecision, the optical paths can automatically return to a home positionat the time of abnormality such as the shutoff of a power source or acontrol signal. The optical switch of the present invention having suchfeature is suitable for optical communications apparatuses, lighttransmission apparatuses, etc.

1-10. (canceled)
 11. An optical switch for switching the connection ofone or more movable optical fibers to one or more stationary opticalfibers, comprising a movable soft magnetic block connected to an endportion of each movable optical fiber, a stationary soft magnetic blockconnected to each stationary optical fiber and fixed at a positionopposing said movable block, an actuator for moving said movable blockrelative to said stationary block, and a means for positioning saidmovable block relative to said stationary block; said actuatorcomprising a yoke having a base portion and a pair of arms extendingfrom both ends of said base portion such that they sandwich said movableblock in its moving direction, a permanent magnet attached to said baseportion of said yoke, and a coil mounted to at least one arm; andregardless of the position of said movable block, a magnetic fluxgenerated by said permanent magnet being more in a first gap between onearm and said movable block than in a second gap between the other armand said movable block.
 12. The optical switch according to claim 11,wherein said first and second gaps have different widths in the movingdirection of said movable block.
 13. The optical switch according toclaim 11, wherein said movable block moves between a home positionclosest to one arm and a make position closest to said other arm;wherein when said coil is energized to generate a magnetic flux, thetotal magnetic flux is less in a first gap between said movable blockand one arm than in a second gap between said movable block and saidother arm, so that said movable block is held at said make position; andwherein when said coil becomes inactive, said movable block returns tosaid home position.
 14. The optical switch according to claim 13,wherein a setback distance δ expressed by δ=(b−s)−a is more than 0,wherein a and b respectively represent the widths of said first andsecond gaps at said home position, and s represents the moving distanceof said movable block.
 15. The optical switch according to claim 11,wherein at least one of said movable block and said stationary block ismade of a soft magnetic ferrite.
 16. The optical switch according toclaim 15, wherein said soft magnetic ferrite is manganese-zinc ferrite.17. The optical switch according to claim 11, wherein said coil ismounted to each arm of said yoke.
 18. An optical switch for switchingthe connection of one or more movable optical fibers to one or morestationary optical fibers, comprising a movable soft magnetic blockconnected to an end portion of each movable optical fiber, a stationarysoft magnetic block connected to each stationary optical fiber and fixedat a position opposing said movable block, an actuator for moving saidmovable block relative to said stationary block, and a means forpositioning said movable block relative to said stationary block; saidactuator comprising a yoke having a base portion and a pair of armsextending from both ends of said base portion such that they sandwichsaid movable block in its moving direction, a permanent magnet fixedbetween said stationary block and said yoke, and one or more coilsmounted to said yoke; said movable block moving between a home positionclosest to one arm and a make position closest to said other arm; thewidth (a+s) of a first gap being smaller than the width (b−s) of asecond gap at said make position, wherein a represents the width of saidfirst gap between said movable block and said one arm at said homeposition, b represents the width of said second gap between said movableblock and said other arm at said home position, and s represents themoving distance of said movable block.
 19. The optical switch accordingto claim 18, wherein the difference (b−a−2s) between the width (a+s) ofsaid first gap and the width (b−s) of said second gap is 0.3 mm or moreat said make position.
 20. The optical switch according to claim 18,wherein said movable block moves between a home position closest to onearm and a make position closest to said other arm; wherein when saidcoil is energized to generate a magnetic flux, the total magnetic fluxis less in a first gap between said movable block and one arm than in asecond gap between said movable block and said other arm, so that saidmovable block is held at said make position; and wherein when said coilbecomes inactive, said movable block returns to said home position. 21.The optical switch according to claim 20, wherein a setback distance δexpressed by δ=(b−s)−a is more than 0, wherein a and b respectivelyrepresent the widths of said first and second gaps at said homeposition, and s represents the moving distance of said movable block.22. The optical switch according to claim 18, wherein at least one ofsaid movable block and said stationary block is made of a soft magneticferrite.
 23. The optical switch according to claim 22, wherein said softmagnetic ferrite is manganese-zinc ferrite.
 24. The optical switchaccording to claim 18, wherein said coil is mounted to each arm of saidyoke.
 25. An optical switch for switching the connection of one or moremovable optical fibers to one or more stationary optical fibers,comprising a movable soft magnetic block connected to an end portion ofeach movable optical fiber, a stationary soft magnetic block connectedto each stationary optical fiber and fixed at a position opposing saidmovable block, an actuator for moving said movable block relative tosaid stationary block, and a means for positioning said movable blockrelative to said stationary block; said actuator comprising a yokehaving a base portion and a pair of arms extending from both ends ofsaid base portion such that they sandwich said movable block in itsmoving direction, a permanent magnet attached to said yoke, and a coilmounted to at least one arm; and said permanent magnet being positionedaway from a longitudinal center line extending between said pair ofarms.
 26. The optical switch according to claim 25, wherein said movableblock moves between a home position closest to one arm and a makeposition closest to said other arm; wherein when said coil is energizedto generate a magnetic flux, the total magnetic flux is less in a firstgap between said movable block and one arm than in a second gap betweensaid movable block and said other arm, so that said movable block isheld at said make position; and wherein when said coil becomes inactive,said movable block returns to said home position.
 27. The optical switchaccording to claim 26, wherein a setback distance δ expressed byδ=(b−s)−a is more than 0, wherein a and b respectively represent thewidths of said first and second gaps at said home position, and srepresents the moving distance of said movable block.
 28. The opticalswitch according to claim 25, wherein at least one of said movable blockand said stationary block is made of a soft magnetic ferrite.
 29. Theoptical switch according to claim 28, wherein said soft magnetic ferriteis manganese-zinc ferrite.
 30. The optical switch according to claim 25,wherein said coil is mounted to each arm of said yoke.